This invention relates to a variable compression ratio system for a two-cycle engine, and more particularly to an improved exhaust control valve therefor.
It has been recognized that engines, and particularly two-cycle crankcase compression engines, may be provided with an exhaust control valve arrangement that controls the timing at which the exhaust port opens and closes. The timing of the exhaust port events can be altered during the engine operation, and this permits adjustment of the engine compression ratio when running. Thus, it is possible to operate a diesel engine at a relatively high compression ratio at low and mid-range speeds to obtain optimum performance. The compression ratio can be reduced at the high-load and high-speed conditions to maintain appropriate temperature control.
Generally, this type of exhaust control valve is a rotary valve that extends transversely through a portion of the exhaust passage adjacent the exhaust port. By rotating the valve, the upper portion of the exhaust port can be selectively obscured, and thus change the timing. In some instances the exhaust control valve is provided in a supplemental exhaust port that merges at its downstream end into the main exhaust passage.
Although these devices are extremely effective, there are some areas where problems can arise. Specifically, the exhaust control valve is subject to accumulating deposits, particularly with two-cycle engines where the exhaust may contain some lubricant. When the engine is shut down, these deposits can solidify due to the temperature elevation which occurs after shutdown and can cause sticking of the valve when the engine is restarted.
There have been proposed arrangements wherein the valve is operated through a cycle or number of cycles, either at shutdown or upon restarting, so as to provide a self-cleaning effect. Although these systems are effective, even they can be improved.
For example, the time at which the self-cleaning operation is performed is quite important. If the self-cleaning operation is done immediately after shutdown, it may be done too early, and deposits can still form after the valve has been cleaned. On the other hand, if the time period before the self-cleaning operation is initiated is too long, then the mechanism for operating the valve may not be strong enough to rotate the valve and effect its self-cleaning.
In addition to the aforenoted problems, self cleaning valves do not themselves attend to another potential problem. That is, in many applications for two cycle engines, for example when used in marine propulsion, the engine may be in an environment where corrosion occur. This is particularly true when operating in marine environments. Corrosion may occur between the valve and the body of the engine in which the valve is journaled. This can occur during periods of long non-use and the self cleaning mechanisms may not be fully capable of cleaning the corrosion and freeing corroded valves.
It is, therefore, a principal object of this invention to provide an improved exhaust control valve for an engine and an operation for permitting manual cleaning thereof.
It is a further object of this invention to provide an improved structure wherein the exhaust control valve of an engine may be manually operated through a mechanical advantage mechanism so as to effect a cleaning operation.
It has been generally the practice to rotatably journal the exhaust control valve directly in the body of the engine in which the exhaust passage is formed. Normally, this is the cylinder block. However, such direct journalling can give rise to some objections.
For example, if wear occurs, then it may be necessary to either rebore the cylinder block and use an oversized valve or resort to some other expedient. In addition, the self-cleaning operation may clean the exhaust valve, but it may not clean the associated portions of the exhaust passage, and buildup may occur adjacent the valve.
It is, therefore, a still further object of this invention to provide an improved exhaust control valve for an engine that facilitates disassembly, servicing, and cleaning.